1. Field of the Invention
The present invention relates generally to an image forming apparatus and, more particularly, to a mounting mechanism for use with mounting components in an optical path of the image forming apparatus.
2. Description of the Related Art
Laser scanning devices may use housings, motors, mirrored polygons or reflective torsion oscillators, lenses, and/or mirrors in order to accomplish their function. Because of the level of accuracy needed, the proper mounting of these components is important. The lenses need to be mounted such that the pointing of the laser beam is properly positioned and the focus of the beam is within its operational limits. In addition to pointing and focusing the laser beam during normal operating conditions, the components need to be mounted so that they are able to withstand common usage conditions, including changes in temperature and humidity. Further, the components need to be able to withstand conditions like vibration and being accidentally dropped.
In the past, mounting of lenses and mirrors was accomplished by a mechanical hardware method that employed screws, clamps, and other types of hardware. While relatively effective, it is not cost efficient. To reduce cost, other methods of mounting the lenses arose, including the use of adhesives to bond the components in place relative to each other.
The use of adhesives is not without its shortcomings, however. Three possible failure modes can arise when adhesives are used to mount lenses and mirrors in the housing of a laser scanning unit. The first mode of failure is a catastrophic loss of the adhesion to the components to which the adhesive is bonded. Because the components are typically made from different materials, each component will expand and contract at a different rate. When this occurs, internal forces develop in the assembly because one component is trying to expand faster than another. So even though components may be of substantially equal length and the forces could be within the range of the adhesive to remain bonded when assembled, when the temperature changes the two different components will have different lengths. When this occurs, the forces that develop from the thermal expansion (and expansion due to humidity) are oftentimes greater than the adhesive's bond to the surface of the components to which it is bonded and the bond breaks, causing a failure. Cycling temperature changes exacerbate the problem by repeatedly generating forces until the material eventually breaks.
The second mode of failure, though less severe, is due to plastic deformation of either the laser scanning unit components or the adhesive itself. This second mode is due to the same root cause, thermal expansion. However, instead of the adhesive bond breaking, the materials plastically deform. What is generally desired is for any deformation to be elastic in nature so that when the forces subside, the components return to their original position. However, if the materials are sufficiently stressed, the components or the adhesive plastically deform, causing beam pointing and/or focus to be outside of operating specifications.
The third failure mode is the least severe but nevertheless causes print defects and is very difficult to compensate for in firmware. Here, there is elastic deformation of the lenses or mirrors due to expansion/contraction. The deformation causes the lenses or mirrors to shift their pointing and/or focus resulting in a print defect.
Based upon the foregoing, there is a need for an improved mounting mechanism for components of the laser scanning unit of an imaging system.